Numerical analysis of effect of static stirring device on mixing uniformity of aerosol in the air duct of a nuclear facility

Abstract

BackgroundDue to the complex structure of the ventilation ducts in nuclear facilities, the concentration distribution of radionuclides such as aerosols in the ducts is uneven. The inhomogeneity of aerosol distribution brings great challenges to the sampling representativeness of radiation monitoring. In chemical processes, static stirring devices are commonly used to enhance the homogeneity of the product mix. However, this device has not been applied in the nuclear power field.PurposeAccordingly, this study aims to improve the mixing uniformity of aerosols in air supply pipelines by using static stirring devices, so as to provide a reference for the representativeness of radiation monitoring sampling.MethodsThe stirring effects of three different stirring devices were investigated through numerical simulations. The RNG k-ε model was used to simulate the gas phase flow field, and the discrete phase model (DPM) was employed in ANSYS CFX software to simulate the behavior of aerosol particles. Selection of the particle size of aerosols followed the recommendations in the sampling representative standards, with the specific size of 10 μm. The other boundary conditions in the simulation were based on the actual operating conditions of a nuclear power plant. As a result, the effects of different stirring devices on the flow field and aerosol concentration distribution were obtained.ResultsThe static stirring device can form strong swirls, thereby improving the uniformity of aerosol distribution. Increasing the twist angle of the blades and the proportion area of the inner blades strengthened the generated vortex field, further affecting the diffusion of aerosols. The static stirring device with an increased inner blade area exhibited a moderate swirl intensity, and better stirring effect than those of the other two structures. The coefficient of variation of the aerosol concentration decreased by 30.60%.ConclusionsInstalling a static stirring device in an air supply duct is a feasible method to improve the mixing uniformity of aerosols. Owing to the complex structure of ventilation ducts in nuclear facilities, the concentration distribution of radionuclides, such as aerosols, in the ducts is uneven. This inhomogeneous aerosol distribution poses significant challenges to the sampling representativeness of radiation monitoring. In chemical processes, static stirring devices are commonly used to enhance the homogeneity of the product mix. However, these devices have not yet been applied in the field of nuclear power.

Keywords

• air supply pipe
• static stirring device
• aerosol
• numerical simulation
• mixing uniformity